1. Field of the Invention
The present invention relates to an image forming apparatus and a process cartridge performing electrostatic copying processes for use in copiers, facsimile machines, printers, etc. and more particularly, to an image forming apparatus and a process cartridge which can remove a toner having a high average circularity.
2. Discussion of the Background
Recently, color image forming apparatuses using electrophotography have been widely used. Almost all the images printed by these apparatuses are digitized before printing and thus a need for an image forming apparatus capable of printing further fine color images exists. It has been attempted to achieve images having a high resolution and a fine gradation using a toner having a high circularity and a small particle diameter.
It is known that a toner having a high circularity and a small particle diameter is precisely transferred and therefore suitable for obtaining a super fine image. However, toner particles having a high circularity tend to diffuse into a space between the cleaning blade used as a cleaner and a photoconductor. Therefore, it is difficult to remove the remaining toner particles on the photoconductor. Thus, the remaining toner particles tend to be transferred to a charger, resulting in contamination of the charging members such as the charging roller, thereby forming faulty images having, for example, uneven density and background development due to uneven charging.
Published unexamined Japanese patent application (hereinafter referred to as JOP) No. 2002-6710 discloses a cleaner containing a blade which accumulates and holds powder at its edge to block spherical toner particles having a form factor of from 100 to 125. Specific examples of such powder are monodisperse silica having a specific gravity of from 1.3 to 1.9 and a particle diameter of from 80 to 300 nm, and magnetic powder having an irregular form or a needle form. However, this device is required to have a powder supply means for supplying powder for blocking toner particles at a portion facing the blade edge or an upstream side therefrom, and a powder accumulating and holding means for blocking spherical toner particles by accumulating and holding powder at the blade edge. That is, the device is complex.
JOP No. 2000-276024 discloses a cleaner which removes remaining toner particles on a movable body. In this disclosure, a discharging means having a roller form is provided at an upstream side from the movable body relative to the moving direction thereof to apply an alternating current voltage while contacting with the movable body. Also a cleaner having a blade is provided at a downstream side from the movable body. The discharging means discharges the movable body and the remaining toner thereon so as to clear the movable body of the remaining toner. In JOP 2002-351279, to remove remaining toner particles on the photoconductor, a fur brush made of a conductive fabric is provided. In addition, a conductive collecting roller which applies a voltage while contacting the fur brush is provided. The remaining toner particles on the photoconductor drum are captured by the fur brush, which rotates while abrading the photoconductor, and are guided to the conductive roller as the fur brush rotates. Then the remaining toner is electrostatically attracted by the conductive collecting roller due to a voltage applied thereto. However, the apparatus has a disadvantage in that the cost increases because a powder supply means and other components have to be provided to apply the voltage.
Further, JOP No. 10-49017 discloses an image forming apparatus including an irradiator, which is provided at the upstream side of a cleaning blade relative to the rotation direction of an amorphous silicone photoconductor drum. This irradiator irradiates a photoconductor drum with light before cleaning to weaken the electrostatic force of toner particles remaining on the photoconductor drum. Then the toner particles remaining on the photoconductor drum are collected by a magnet roller and the collected toner particles are recycled, re-supplied and used for developing a latent image on the photoconductor. However, the technology disclosed is to prevent the photoconductor from deteriorating due to the abrasion caused by a single component magnetic toner held on a magnet roller. Therefore, it is difficult to apply this technology to a double component developer for use in forming color images.
For the above reasons, the need exists for a relatively simple image forming apparatus capable of producing further fine color images.